Radiation-emitting semiconductor component

ABSTRACT

A radiation-emitting semiconductor component with a layer structure ( 12 ) which includes a photon-emitting active layer ( 16 ), an n-doped cladding layer ( 14 ) and a p-doped cladding layer ( 18 ), a contact connected to the n-doped cladding layer ( 14 ) and a mirror layer ( 20 ) connected to the p-doped cladding layer ( 18 ). The mirror layer ( 20 ) is formed by an alloy of silver comprising one or more metals selected from the group consisting of Ru, Rh, Pd, Au, Os, Ir, Pt, Cu, Ti, Ta and Cr.

The invention relates to a radiation-emitting semiconductor component inaccordance with the preamble of patent claim 1.

It relates in particular to a radiation-emitting semiconductor componenthaving a layer structure which includes a photon-emitting active layer,an n-doped cladding layer and a p-doped cladding layer, and n-contactconnected to the n-doped cladding layer and a mirror layer connected tothe p-doped cladding layer.

This patent application claims the priority of German Patent ApplicationNo. 102 44 200.2, the content of disclosure of which is herebyincorporated by reference.

Radiation-emitting semiconductor components, such as for exampleInGaN-based top-down mounted luminescence diodes or thin-filmluminescence diodes require highly reflective mirror materials whichreflect radiation emitted from the active zone toward the component rearside back toward the front side or toward the component flanks.

In the case of top-down mounted luminescence diodes, theradiation-generating epitaxial layer sequence faces toward the mountingside, i.e. the component radiates through the growth substrate if stillpresent. In the case of thin-film luminescence diodes, the growthsubstrate used for the epitaxial growth of the radiation-generatingepitaxial layer sequence is at least partially removed and the epitaxiallayer sequence is located on a carrier substrate applied subsequently.

Furthermore, for luminescence diodes based on nitride III-V compoundsemiconductor material, in particular based on GaN, such as AlGaN, InGaNand InGaAlN, and also GaN itself, the mirror materials are to form anohmic contact with the p-doped layer of the layer structure.

The problem in this context is that metals of good reflective propertiesin the blue spectral region, such as aluminum, do not form an ohmiccontact on p-GaN or related materials, such as p-AlGaN, p-InGaN andp-InGaAlN. On the other hand, materials which form a good contact onp-GaN, such as for example platinum or palladium, have an adsorbingaction in the blue spectral region and are therefore not suitable foruse as mirror material. Only silver is both sufficiently reflective andsuitable for the contact-connection of p-GaN, etc. However, the drawbackin this case is that the mechanical stability of silver layers isinsufficient for use in luminescence diodes.

The group of radiation-emitting components based on nitride III-Vcompound semiconductor material in the present case include inparticular chips in which the epitaxially produced semiconductor layer,which typically includes a layer sequence composed of various individuallayers, includes at least one individual layer which comprises amaterial from the nitride III-V compound semiconductor material systemIn_(x)Al_(y)Ga_(1-x-y)N, with 0≦x≦1, 0≦y≦1 and x+y≦1. The semiconductorlayer may, for example, have a conventional pn junction, a doubleheterostructure, a single quantum well structure (SQW structure) or amultiple quantum well structure (MQW structure). Structures of this typeare known to the person skilled in the art and are therefore notexplained in more detail at this point.

The choice of mirror material is also difficult in the case ofshort-wave thin-film luminescence diodes based on InGaAlP. Gold, whichis often used as mirror material at present, limits the efficiency ofthese diodes, on account of its relatively low reflectivity. Silver,which is more suitable in terms of reflectivity, has not hitherto beenused, on account of its poor bonding and on account of migrationproblems.

One approach aimed at eliminating these difficulties consists in usingaluminum mirrors, in which the electrical terminal is formed by aplatinum layer and the optical properties are provided by the aluminum.Alternatively, it is possible to deposit silver which is fixed to a sidefacing away from the wafer by further metals.

The present invention is based on the object of providing aradiation-emitting semiconductor component of the type described in theintroduction having an improved mirror layer and thereby of increasingthe efficiency and performance of these components.

This object is achieved by a radiation-emitting semiconductor componenthaving the features of patent claim 1. Advantageous configurations andrefinements are given in subclaims 2 to 13.

According to the invention, in a radiation-emitting semiconductorcomponent of the generic type, the mirror layer is formed by an alloy ofsilver with one or more metals selected from the group consisting of Ru,Rh, Pd, Au, Os, Ir, Pt, Cu, Ti, Ta and Cr. The addition of these metalsmakes it possible to significantly improve the mechanical properties ofsilver layers without reducing the reflectivity of the layer compared topure silver. At the same time, the diffusion of silver into theadjoining semiconductor layer is reduced.

In one preferred configuration of the radiation-emitting semiconductorcomponent according to the invention, the mirror layer is formed by analloy of silver with one or more metals selected from the groupconsisting of Ru, Rh, Pd, Au, Os, Ir, Pt and one or more metals selectedfrom the group consisting of Cu, Ti, Ta, Cr. Ternary alloys of thisnature have both a high reflectivity in the desired short-wave spectralregion and a sufficient mechanical stability.

It is considered particularly preferable for the mirror layer to beformed by an Ag—Pt—Cu alloy. This alloy combines a high reflectivity inthe blue spectral region with a high mechanical and thermal stability.

It is advantageously provided in this context that the alloy of thesilver layer, in addition to silver, comprises a total of 0.1% by weightto 15% by weight, preferably 1% by weight to 5% by weight, of theabovementioned metals.

In a preferred refinement of the radiation-emitting semiconductorcomponent according to the invention, it is provided that the alloy ofthe mirror layer, in addition to silver, comprises 0.5 to 5% by weightof one or more metals selected from the group consisting of Ru, Rh, Pd,Au, Os, Ir, Pt and 0.5 to 5% by weight of one or more metals selectedfrom the group consisting of Cu, Ti, Ta, Cr.

In this context, the alloy of the mirror layer of the radiation-emittingsemiconductor component comprises in particular, in addition to silver,1 to 3% by weight of platinum and 1 to 3% by weight of copper.

In an expedient refinement of the invention, the mirror layer forms anohmic contact with the p-doped cladding layer, so that the mirror layercan simultaneously perform the function of a p-contact layer.

The configuration of the mirror layer according to the invention isparticularly suitable for use in radiation-emitting semiconductor chips,in particular thin-film light-emitting diode chips, in which theradiation-generating layer structure is based on InGaAlN or InGaAlP. Inparticular, ohmic contacts can be produced using silver-containingalloys for InGaAlN-based luminescence diodes. Therefore, the mirrormetallization can be produced directly above a light-generating layer.

A thin-film light-emitting diode chip is distinguished in particular bythe following characteristic features:

-   -   a reflective layer is applied to or formed on a first main        surface, facing a carrier element, of a radiation-generating        epitaxial layer sequence, the reflective layer reflecting at        least some of the electromagnetic radiation generated in the        epitaxial layer sequence back into the latter;    -   the epitaxial layer sequence has a thickness in the range of 20        μm or below, in particular in the region of 10 μm; and    -   the epitaxial layer sequence includes at least one semiconductor        layer with at least one surface which has a mixed structure        which ideally leads to an approximately ergodic distribution of        the light in the epitaxial layer sequence, i.e. it has as far as        possible ergodically stochastic scattering properties.

A basic principle of a thin-film light-emitting diode chip is described,for example, in I. Schnitzer et al., Appl. Phys. Lett. 63 (16), Oct. 18,1993, 2174-2176, the content of disclosure in this respect is herebyincorporated by reference.

A thin-film light-emitting diode chip is, to a close approximation, aLambert radiator and is therefore particularly suitable for use in aheadlamp.

In the present context, the term “radiation-generating layer structurebased on InGaAlP” means that a layer structure designated as such orpart of a layer structure of this type preferably comprisesAl_(n)Ga_(m)In_(1-n-m)P where 0≦n≦1, 0≦m≦1 and n+m≦1. This material doesnot necessarily have to have a precise mathematical composition inaccordance with the above formula. Rather, it may also include one ormore dopants and additional constituents which leave the physicalproperties of the material substantially unchanged.

In the present context, the term “radiation-generating layer structurebased on InGaAlN” means that a layer structure designated as such orpart of a layer structure of this type preferably comprisesAl_(n)Ga_(m)In_(1-n-m)N, where 0≦n≦1, 0≦m≦1 and n+m≦1. This materialdoes not necessarily have to have a mathematical composition preciselyin accordance with the above formula. Rather, it may include one or moredopants and additional constituents which leave the physical propertiesof the material substantially unchanged.

Further advantageous configurations, features and details of theinvention will emerge from the dependent claims, the description of theexemplary embodiment and the drawing.

The invention is explained in more detail below on the basis of anexemplary embodiment in conjunction with the drawing, which illustratesin each case only the elements which are of relevance to gaining anunderstanding of the invention. In the drawing:

FIG. 1 shows a diagrammatic sectional illustration of aradiation-emitting semiconductor component in accordance with anexemplary embodiment of the invention.

FIG. 1 shows a diagrammatic sectional illustration of an InGaNluminescence diode 10 which emits in the blue spectral region. Theluminescence diode 10 includes a layer structure 12 comprising ann-doped cladding layer 14, a photon-emitting active layer 16 and ap-doped cladding layer 18.

An n-contact 22 is arranged on the n-doped cladding layer 14 for thepurpose of supplying current. In the exemplary embodiment, the p-contactis formed by the p-contact layer 20, which simultaneously forms a highlyreflective mirror layer which reflects the component of the radiationgenerated by the active layer 16 in the direction of the mirror layer.

In the exemplary embodiment, the mirror layer 20 consists of an AgPtCualloy containing approximately 1.5% by weight of platinum andapproximately 1.5% by weight of copper. This alloy on the one hand formsa good ohmic contact with the p-GaN cladding layer 18. Furthermore, theaddition of platinum and copper to silver significantly improves themechanical properties of the silver layer. The high reflectivity of themirror layer in the blue spectral region is retained. Furthermore, thereis scarcely any diffusion of silver atoms out of the AgPtCu layer 20into the p-doped cladding layer 18, and as a result a highly reflective,stable p-contact layer is obtained.

A mirror layer of this type formed from an AgPtCu alloy is furthermorealso suitable for use in InGaAlP thin-film luminescence diodes, where,as a highly reflective and thermally stable metal mirror, it contributesto increasing the efficiency of the LEDs. Alternatively, the mirrorlayer may consist of an AgPtRhCu alloy, an AgPtCuTi alloy or anAgPtRhCuTi alloy or another of the advantageous alloys listed in thegeneral part of the description.

The features of the invention which are disclosed in the abovedescription, in the drawing and in the claims may be pertinent to therealization of the invention both individually and in any desiredcombination.

1. A radiation-emitting semiconductor component, having a layerstructure (12) which includes at least one photon-emitting active zone(16) arranged between a cladding layer (14) that is n-conductively dopedand a cladding layer (18) that is p-conductively doped, an n-typecontact connected to the cladding layer (14) that is n-conductivelydoped, and a mirror layer (20) arranged on the side, facing away fromthe active zone (16), of the cladding layer (18) that is p-conductivelydoped, wherein the mirror layer (20) is formed by an alloy of silvercomprising one or more metals selected from the group consisting of Ru,Os, Ir, Cu, Ti, Ta and Cr.
 2. The radiation-emitting semiconductorcomponent as claimed in claim 1, wherein the mirror layer (20) is formedby an alloy of silver comprises one or more metals selected from thegroup consisting of Ru, Rh, Pd, Au, Os, Ir, Pt and one or more metalsselected from the group consisting of Cu, Ti, Ta, Cr.
 3. Theradiation-emitting semiconductor component as claimed in claim 1,wherein the mirror layer (20) is formed by an alloy of silver comprisinga metal selected from the group consisting of Ru, Rh, Pd, Au, Os, Ir, Ptand one or more metals selected from the group consisting of Cu, Ti, Ta,Cr.
 4. The radiation-emitting semiconductor component as claimed inclaim 1, wherein the mirror layer (20) is formed by an alloy of silvercomprising one or more metals selected from the group consisting of Ru,Rh, Pd, Au, Os, Ir, Pt and a metal selected from the group consisting ofCu, Ti, Ta, Cr.
 5. The radiation-emitting semiconductor component asclaimed in claim 1, wherein the mirror layer (20) is formed by an alloyof silver comprising a metal selected from the group consisting of Ru,Rh, Pd, Au, Os, Ir, Pt and a metal selected from the group consisting ofCu, Ti, Ta, Cr.
 6. The radiation-emitting semiconductor component asclaimed in claim 1, wherein the mirror layer (20) is formed by anAg—Pt—Cu alloy.
 7. The radiation-emitting semiconductor component asclaimed in claim 1, wherein the alloy of the mirror layer (20), inaddition to silver, comprises a total of 0.1% by weight to 15% byweight, said metals.
 8. The radiation-emitting semiconductor componentas claimed in claim 2, wherein the alloy of the mirror layer (20), inaddition to silver, comprises 0.5 to 5% by weight of one or more metalsselected from the group consisting of Ru, Rh, Pd, Au, Os, Ir, Pt and 0.5to 5% by weight of one or more metals selected from the group consistingof Cu, Ti, Ta, Cr.
 9. The radiation-emitting semiconductor component asclaimed in claim 6, wherein the alloy of the silver layer (20), inaddition to silver, comprises 1 to 3% by weight of platinum and 1 to 3%by weight of copper.
 10. The radiation-emitting semiconductor componentas claimed in claim 1, wherein the mirror layer (20) forms an ohmiccontact either with the cladding layer (18) that is p-conductively dopedor with a further semiconductor layer that is p-conductively doped andis arranged between the mirror layer and the cladding layer (18) that isp-conductively doped.
 11. The radiation-emitting semiconductor componentas claimed in claim 1, wherein the layer structure (12) is based onnitride III-V compound semiconductor material.
 12. Theradiation-emitting semiconductor component as claimed in claim 11,wherein the layer structure (12) is based on InGaAlN.
 13. Theradiation-emitting semiconductor component as claimed in claim 1,wherein the layer structure (12) is based on phosphide III-V compoundsemiconductor material.
 14. The radiation-emitting semiconductorcomponent as claimed in claim 13, wherein the layer structure (12) isbased on InGaAlP.
 15. The radiation-emitting semiconductor component asclaimed in claim 1, wherein the alloy of the mirror layer (20), inaddition to silver, comprises a total of 1% by weight to 5% by weight ofsaid metals.
 16. The radiation-emitting semiconductor component asclaimed in claim 1, wherein the mirror layer comprises a ternary alloyof silver.